Process of manufacturing leather and products used in connection therewith



Patented I May 15, 1934 1,959,112 'raoosss on momoronmc mum AND,PRODUCTS US WITH THERE Charles G. Shaw, Huntsville,

ED IN CONNECTION and {was Honman, Toronto, Ontario, Canada No Drawing.Application November Serial No. 496,032. Renewed January 17,193;

This invention relates to aprocess of" applyin coating materials tovegetable tanned leather and more especially to the application of suchmaterials to sole leather suioseintently to the compacting of theleather but prior tosuch finishing operations as third rolling and/orbrush- Moreparticularly, the present invention relates to a furtherdevelopment of the subject matter 1 disclosed in our. co-pendingapplication Serial No.

459,103, filed June coveries set forth in the above-mentionedapplication and in our co-pending application Serial No. M910 filed June3rd, 1930, in connection 1 with the application oi coating materials tovegetable tanned leather, such materials when applied to the grain ofvegetable tanned leather which had previously been filled with suchmaterials as wax, resin, oil, tanning extract, sugar, 26 and the like,for thepurpose of rectifying the unpleasant colour caused-by thefilling, would lack adhesion and would be removed by subsequentoperations in the shoe factory, where it is I thepractice to soak theleather in water, thus exposing the unpleasant colour beneath.

In our application Serial No. 459,103 referred to above, wehavedescribed a; process which overcomes this difiiculty and provides afinish which satisfactorily adheres to the leather-throughout 30 all thesubsequent operations to which it is normally submittedeither in theprocess of finishing the manufacture or in being worked in the shoefactory. However, the rather rough treatment to which the coating issubjected in the process of setting out, jacking, rolling, etc. makes itnecessary to apply quite a substantial film'of material in order that itmay withstand the simple wear of the smoothening and finishingoperations and at times, if this abrasion is excessive, an additionalcoating of material has to be applied to bring back the freshness ofappearance after the mechanical operations are completed, This-may.

have a tendency to impart to the surface of the finished leather 2..painty appearance and the operations of rolling and pressing after'thecoat-f ing material is applied may result in a darken- -ing of thecolour of the leather which is ordinarily corrected in the case'ofuncoated leather by the use of so-called spon ing compounds" of whichthere are many on the market, 'consisting mainly of a slightly alkalineaqueous solution of soaps and sulphonated oil and into which the leatherafter compaction is quickly dipped,

and then dried. Subsequently, when theleather 5 is thoroughly dry, it isthe usual custom to sub- 3rd, N30. Prior to our dis-- unit it to theoperation known as third rolling which restores the gloss withoutdarkening the.

colour.

wine of the objects of this invenfion is the application of an adhesivefilm subsequent to the til compacting operations, such film being sothinthot while it is sumclent' to render the leather uniform in colourit is insuficiently thick to plug the hair holes.

Another object of this invention is the production of sole leatheruniform in colour but or ex tremely rapid and uniform soamngcharacteristics during the tempering operations in the shoe factory. V

our application Serial No. ass-nos we showed to that if the coatingmaterials were applied. after the-operations oi compacting and theleather, adhesion would he unsatisfactory owing to the glazing oithehyaline layer and the'plugsing oi the hair holes. The "theory underlying.siuch results is that it is the condition of glaze or unglaze oi thesurface of the leather or hyaline layer which regulates its absorptivecapacity for colloidal matter and thus controls the tendency to adhesionof coating materials applied to, it. so This explanationis based uponthe fact that satisfactory adhesion, so far as we have been able toascertain has never been obtained by the simple application of thecoating materials to leather which has only-been rolled, jacked, set outI or pressed and many attempts to remove the glossing effects of theseoperations have been made without rendering the leather in suchcondition that satisfactory adhesion of the coating materials wouldresult. Simple sponging or washing with water or with the usual spongingcompounds was ofno avail as, although the appear-- ance of gloss wasremoved, coating material applied lacked adhesion and was readilyremoved when the leather was resoaked. Similarly washing the leatherwith alternate solutions of acids and alkalies gave unsatisfactoryresults. On the other hand, finished leather'when bleached and oiledlightly in a drumming operation would have its surface finish removedand when dried in the, usual manner could be coated with showingsatisfactory adhesion. After such treatment, however, the leather had tobe once more to the complete mechanical operations of finishing in orderto restore the appearance of finished leather. we have now found thatthe objectionable condition of thethyaline layer after the leather hasbeenrolledandpressedcanberemovedbywashingtheleathetflrstin a dilutealkali solution and then in a dilute acid solution such acid solutionpreferably containing a sulphonated oil of a type which is compatiblewith the acid solution used.

The leather is then dried and the finishing mate- 5 rials applied.

As an example of the manner in which we carry out our invention, theleather is finished and dried and brought to a condition ready for theapplication of the sponging compound as already described earlier inthis specification. It is, however, not treated with the spongingcompound but instead is washed on the grain side by applying a solutioncontaining 2% of borax in water at a temperature of about 160 F; to 180F. This application is conveniently carried out by means of a harnessleather. blacking machine. The leather is then passed quickly through asolution of a weak organic acid, such as acetic or lactic acid, thestrength of the solution being such as to neutralize the efiect of thealkali treatment which has darkened the leather, and thus rectify andlighten the colour in much the same 'manner. as is done in the ordinaryopera- 1 tion for bleaching the leather. To the acid solution is-addedabout 2% of a sulphonated oil of such a nature that it is not 'readilythrown out of solution by the acid. sulphonated but not neutralized, areexamples of the sulphonated oils which we may employ. The

: leather after being dfied is now ready for coating.

The materials we prefer are first a priming coat containing pyroxalinand a heavy bodied China woodoil in the proportions of about one part ofthe former to three parts of the latter made up in the usual lacquersolvents to contain about 12% of solids. This primer is mixed with anequal volume of thinner consisting of the same solvents and is verylightly sprayed on the grain surface of the leather, one gallon of themixture covering about 300 to 500 sq. feet of surface. After the primerhas dried a short time the pigmented coating is applied. This coatingcomposition has the general composition:-

- Per cent 5 Pigment 12.8

. Pyroxyl I 6.0 Dibutyl phthalate 2.5 Neats-foot nil 1.4 Butyl acetate20.3

Ethyl acetat 24.0 Tnlnnl 27.0

the nature of the pigment being varied in ac- 5 cordance with the colourrequired.

This material is reduced with thinner and a very'fine or mist 'coat isapplied just suflicient to impart a uniform appearance to the surface ofthe leather. After the coatedmaterial has dried a fine coating of a waxemulsion is sprayed upon the top of the coating composition. This waxemulsion is prepared by melting together two parts of carnauba wax andone part of ceresine wax and slowly stirring in one part of sul- C5phonated castor oil. The mixture is then diluted with water, run througha colloid mill and again diluted with water to the desired sprayingconsistency. After the wax coating has dried, the

leather is third rolled and brushed. As the 73 customary brass rollingball and bed have a tendency to mark the coating, a steel ball or onechromium plated is preferably used and over comes this difficulty.

We wish it to be understood that we do not con- 7 fine ourselves to theexact details as outlined in Acidopole fish oil the'above example, asmany modifications can be made without departing from the spirit of thisinvention. For instance, the temperatures of the alkali and acidsolutions .used can be varied considerably. The alkali solution can beused at room temperature orlat any temperature up to that at which itmight damagejhe leather or down to that at which its action upon theleather would be so slow as to demand a prolonged soaking. Similarly theacid solution may be used at any convenient temperature up to that atwhich the oil will not stay properly in solution or the leather beharmed by the hot water.

Again we may introduce into the alkali solution a small percentage(about 1%) of an ordinary sponging compound into which the leather maybe clipped and subsequently treated with an acid solution from which thesulphonated oil has been omitted, subsequently spraying or swabbing onabout a 5% solution of sulphonated oil'or such emulsifiable mineral oilsas are obtained by the addition of triethanolamine soap. We have foundthat the action of such oil is to prevent the hyaline layer frombecoming harsh or tinny and aids in securing satisfactory adhesion.

We also wish to point out other alkalies may be used in place of theborax referred to. For instance, sodium or potassium hydrates,carbonates or bicarbonates may be used although we prefer borax onaccount of its less vigorous action on the leather.

Similarly other acids than acetic or lactic may be employed, such asoxalic, sulphurous, sulphuric, and other common organic or inorganicacids but, as some of these harm the leather unless used with caution,we prefer to. use acetic or lactic as they are more normal to thetannage of leather.

Further, third rolling or brushing" are not essential to the successfulcarrying out of our invention although the waxing and brushing greatlyimprove the quality of the finished surface.

We have found that treatment such as that described above is essentialif satisfactory adhesion of the coating materials to leather which hasalready been compacted is to be obtained. It is necessary that thehyaline layer or surface of the leather should be cleansed and held openuntil the coating materials are applied and we ,have found that theordinary sponging compounds applied as such do not accomplish this Iend. They leave a heavy residue which it has been proven does notfunction. Borax and the like satisfactorily prepare. thehyaline layerbut darken and stain the surface, whose colour is only properly restoredby the subsequent action of the acid which, however, without thetreatment with sulphonated or similar oil assumes a harsh characterwhich it is necessary to overcome if the natural appearance andcharacterof the leather is to be fully restored. This is accomasagna Vegetabletanned leather, such as harness leather or sole leather, finished inaccordance with the present invention does not bruise or change colouron scufling or rubbing. It has a very high degree of uniformity of-colour and an excellently natural appearance due to the fact that thealkali-acid treatment produces a light and uniform colour which enablesa minimum of coating materials to be applied and thus does not detractfrom the natural appearance of the leather itself.

This minimum of coating materials also-means that the leather hasexcellent soaking properties and in this respect is superior to thatproduced by either of the processes described in our copendingapplications. In fact we have produced by this process leather whichwill soak satisfactorily for working in the shoe factory in from 3 to 10seconds immersion in water which is of considerable importance inconnection with some of the or more coatings of waterproof material tothe leather in such amanner as not to plug the hair holes.

3. A process of manufacturing leather which includes the steps oftreating the grain surface of the leather as in claim 1, and thenapplying a priming composition containing a pyroxylin and heavy bodiedChina wood oil dissolved in suitable solvents, and a second coating of acomposition containing pyroxylin, neats-foot oil and a pigment orcolouring matter. I

4. A process of manufacturing leather which includes the steps oftreating the grain surface of the leather as in claim 1, then applyingone or more fine coats of waterproof material in such a manner as not toplug the hair holes, and then applying a coating of a wax emulsion andsubsequently third rolling" and/or brushing the leather.

5. A process of manufacturing leather which includes the steps oftreating the grain surface of vegetable tanned leather, subsequent tothe com-.

pacting operation, with a solution of alkali folhated oil.

lowed. by treatment wit an acid and a sulpho- 6. The herein describedprocess of applying coating materials to vegetable tanned leather following compacting of the leather but prior to such finishingoperations'as third rolling and/or brushing, said process comprising thefollowing steps 1) washing the leather in a dilute alkaline solution (2)subjecting the washed leather to the action of a solution of a weakorganic acid containing a small percentage of a sulphonated oil which iscompatible with the particular acid solution used, the strength of saidacid solution being suflicient to offset the darkening effect exerted onthe leather by the alkaline treatment (3) spraying onto the grainsurface of the leather a priming coat containing pyroxylin and a heavybodied Chinawood oil dissolved in suitable solvents (4) permitting thepriming coat to dry and (5) applying to the previously coated surface asecond coating of a composition containing pyroxylin and coloringmatter.

7. The herein described process of applying coating materials tovegetable tanned leather following compacting of the leather but priorto such finishing operations as third rolling and/or brushing, saidprocess comprising the following steps 1) subjecting the leather to theaction of a dilute alkaline solution containing a small percentage of anordinary sponging compound (2) treating the leather with a solution of aweak organic acid of suflicient strength to neutralize the darkeningeffect of the alkaline treatment (3) treating the leather withsulphonated oil to prevent the hyaline layer becoming harsh and topromote adhesion of subsequently applied coating materials (4) thenapplying to the leather one .or more coating compositions containingpyroxylin dissolved in suitable solvents.

8. Vegetable tanned leather, to the grain surface of which has beenapplied one or more adhesive layers of a composition comprising acellucharacterized by being uniform in color and ca.-

pable of being satisfactorily and uniformly soaked in water in from.3 to10 seconds. 4

, CHARLES G. SHAW.

JACQUES HOFFMAN.

